On Tue, Feb 16, 2016 at 4:33 AM, David Wragg <david@weave.works> wrote: > Jesse Gross <je...@kernel.org> writes: >> On Wed, Feb 10, 2016 at 3:21 PM, Tom Herbert <t...@herbertland.com> wrote: >>> On Wed, Feb 10, 2016 at 12:59 PM, Jesse Gross <je...@kernel.org> wrote: >>>> On Wed, Feb 10, 2016 at 12:41 PM, David Wragg <david@weave.works> wrote: >>>>> Tom Herbert <t...@herbertland.com> writes: >>>>>> The correct thing to do is determine the maximum amount of >>>>>> encapsulation overhead that can ever be set in a packet and use for >>>>>> setting the MTU. For instance, when RCO is enable in GUE, the size of >>>>>> the option is included in tunnel->encap_hlen even though it will not >>>>>> be used in all packets (via ip_tunnel_change_mtu). If there is no way >>>>>> to determine a maximum overhead a priori from configuration, then >>>>>> maximum overhead could be assumed to be maximum possible encapsulation >>>>>> header size which for Geneve is 132 bytes IIRC. >>>>> >>>>> Ok, I'll come up with a patch to address this. >>>> >>>> I don't think that this really applies in this situation. The concerns >>>> here relate to what the MTU is actually set to but this patch affects >>>> the range of MTUs allowed to be set by the user. I don't see a reason >>>> to disallow the user from setting a precise value if they know what it >>>> should be. >>>> >>> Right, but if the user sets a bad value and packets are silently >>> dropped on the floor then that seems like a bad result that could have >>> easily been prevented. >> >> Sure, we might as well prevent the extreme edge cases that can never >> be valid. In the case of Geneve though, this would be the minimum >> header size, not the maximum, since it's possible that the user >> actually knows how big the options are that they want to use. >> >> But as I said, the practical impact is low because IP_MAX_MTU is so >> much larger than the MTU of real devices. There will always be many >> values that the MTU can be set to that result in dropped packets. This >> is true of all tunnel types. > > I agree with Jesse, and if there was a debate about lifting the MTU > limit on all tunnel types to IP_MAX_MTU, I'd be for that. > > But for the other tunnel types, I followed the precedent of the code > that was already there, and geneve might as well be consistent. > Please implement like in ip_tunnel_change_mtu (or better yet call it), that is the precedent for tunnels.
Tom > Patch sent to the lists. > > David
